Solvent refining lubricating oils with n-methyl-2-pyrrolidone



Oct. 14, 1969 H. C. MoRms ETAL soLvEN'r REFINING LUBRICATING oILs WITH N-METHYL-2-PYRROLIDONE Original Filed March 13. 1967 AID United States Patent O U.S. Cl. 208-36 4 Claims ABSTRACT F THE DISCLOSURE Manufacture of lubricating oil product by distillation of crude oil effecting separation of a lubricating oil stock, refining lubricating oil stock for the removal of constituents of low viscosity index, low thermal stability, and poor oxidation stability by solvent extraction with a solvent comprising N-methyl-Z-pyrrolidone at conditions effective to dissolve at least ten volume percent of said lubricating oil stock producing, as a raffinate, a refined lubricating oil stock of improved viscosity index, thermal stability, and oxidation stability, dewaxing refined lubricating oil stock effecting formation of a lubricating base oil of low pour point, and blending dewaxed lubricating base oil with inhibitor forming a lubricating oil product.

This application is a continuation of Ser. No. 624,971 filed Mar. 13, 1967 and now abandoned.

BACKGROUND OF THE INVENTION Plield of the invention In the manufacture of lubricating oils from crude pe'- troleum one or more fractions containing the lubricating oil constituents are separated by distillation, usually by vacuum distillation. The raw lubricating oil fractions contain unstable naturally occurring materials which tend to form deposits or become corrosive in operating equipment as a result of heating and oxidation or both. Additionally, in the case of paraflinic oils, it is often desirable to increase| the viscosity index by removing the more aromatic lower viscosity index constituents from the oil. To accomplish this it is necessary to remove or destroy a significant amount of material present in the raw stock, typically ranging from to 60 percent depending on the qualities desired in the product oil. The most common way to do this is by extraction with a solvent having selectivity for the more unstable molecules which are predominantly aromatic and non-hydrocarbon materials. Prior to the advent of solvent extraction, severe treatment with concentrated sulfuric acid lwas commonly used to destroy these undesirable materials.

In the treatment of oils to remove unstable, corrosive, and low viscosity constituents of oil, a substantial amount 'of material is removed from the charge stock, that is, an

amount in excess of about 10 volume percent. This is distinctly different from decolorizing treatment in lubri- ACC eating oil manufacture where only trace amounts of coloring material are removed, typically less than 1.0 percentrHere, handling losses are usually greater than the amount of material removed. Common methods used for color improvement are, for example, clay treating, mild acid treating and hy-finishing (mild hydrogenation). Such color improvement steps are often used after solvent refining. A raw stock that is only treated for color improvement is usually unsatisfactory as regards thermal and oxidation stability or viscosity index. Lubricating oil stocks are also frequently treated to remove wax to reduce the cloud point or pour test.

This invention is directed to the manufacture of lubricating oils by the sequence of distillation, solvent extraction using N-methyl-Z-pyrrolidone as selective solvent, ,referred to hereinafter for brevity as NMP, dewaxing, inhibitor addition, and blending. The solvent extraction with NMP is effected at a temperature of at least 50 F. and below the temperature of complete miscibility of the lubricating oil stock in NMP and at a dosage effective to dissolve at least 10 volume percent of said lubricating oil stock whereby a refined lubricating oil stock is produced of improved viscosity index, improved thermal stability, and improved oxidation stability.

Description of the prior art Heretofore NMP has been known as a solvent for the separation of olefins, diolens, and aromatic hydrocarbons. It is also known that NMP may be used to treat ,oil for improvement of color. However, it has not been known that NMP is an effective solvent for the separation of constituents of low thermal and oxidation stability from ilubricating oil fractions and for the separation of low viscosity index constituents from lubricating oil.

SUMMARY OF THE INVENTION In accordance with this invention, finished lubricating oils are produced from crude oil by vacuum distillation, solvent refining of the vacuum distillate with NMP as a selective solvent, dewaxing, and inhibitor addition without theI necessity of conventional finishing treatments such as hy-nishing, clay, and acid treating. In the solvent refining step, the vacuum distillate lubricating oil stock is contacted with NMP at a temperature of at least 50 F. and below the temperature of complete miscibility of said lubricating oil stock in NMP and at `a dosage effective to dissolve at least l0 volume percent of said lubricating oil stock. The foregoing solvent extraction step produces a refined lubricating oil stock of improved viscosity index, improved thermal stability and improved oxidation stability. The manufacture of a merchantable paraffin base lubricating oil from the refined lubricating oil stock necessitates only removal of wax by dewaxing means well known in the art and the addition of inhibitorsy to produce a stock of high oxidation and thermal stability. Obviously, naphthene base oils do not require dewaxing `and only the addition of usual inhibitors Iis necessary.

Solvent extraction with NMP may be applied to paraffin base oils, for example, oils used in the manufacture of crankcase lubricants for internal combustion engines, Iand naphthenie oils, for example, oils used in the manufacture of turbine lubricating oils. In the case of paraffin base oils, an extraction temperature within the range of about 120 to 250 F. and preferably within the range of about 140 to 180 F. is employed and a solvent dosage within the range of 50 to 450 percent and preferably 100 to 340 percent is employed. The corresponding extraction temperatures and dosages when refining naphthene oils are within the range of 50 to 200 F., preferably within the range of 75 to 150 F. and 50 to 300 percent, and preferably 75 to 200 percent respectively. Significantly the' dosage of solvent employed is only about half that employed with furfural, a widely used selective solvent. Typically the viscosity index of paraffin base lubricating oil charge stocks is within the range of about 40 to 105 and the viscosity index of the refined lubricating oil stock is at least l units higher.

Solvent refined paraffinic oils typically contain substantial amount of wax which causes the oil to have a high pour test and high cloud point. The manufacture of low pour test lubricating oils requires the removal of such waxy materials which may be effected by the well known methylethylketone-toluol solvent dewaxing process. In the dewaxing process, the Wax bearing oil is diluted with an MEK-toluol solvent mixture. The diluted oil mixture is then chilled to a temperature at which the wax is precipitated as solid crystals. The wax is separated by filtration and the oil is then separated from the solvent by distillation to produce a finished dewaxed refined oil of low pour test.

BRIEF DESCRIPTION OF DRAWINGS The figure shows a block diagram of the processing sequence which may be used in the manufacture lubricating oils in accordance with the process of this invention. Crude oil in line 1 is passed to crude distillation facility 2. In crude distillation facility 2, the crude oil is separated into lower boiling fractions, for example gas, fuel distillates, and gas oils, discharged through line 3, lubricating oil distillates discharged through line 5 and crude residuum discharged through line 4. The lubricating oil distillate in line 5 is passed to NMP solvent extraction facility 6 wherein the lubricating oil distillate is contacted with NMP affecting separation of lube extract which is discharged through line 7. Rafinate product comprising solvent refined lubricating oil is discharged through line 8 to dewaxing facility 9. In dewaxing facility 9, waxy constituents are removed and discharged through line 10. Dewaxed refined oil is discharged through line 11, combined with inhibitor from line 12, and passed through line 13 to lubricating oil product blending.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example I In a specific application of this invention, a lubricating oil stock, referred to as Wax Distillate 20, is separated from crude oil by vacuum distillation. Tests on the Wax Distillate 20 includes a SUS viscosity at 100 F. of 430, a SUS Viscosity at 210 F. of 56.0, a viscosity index of 73.5, a Lovibond color V2" cell of 580 and a refractive index at 70 C. of 1.4820. The Wax Distillate 20 is extracted n a single stage batch extraction apparatus using NMP as a solvent and a parallel extraction is made with furfural at the conditions and with the results shown in Table I following:

TABLE I.-CONDIT[ONS Solvent Furfural NM 1 Solvent dosage, percent 200 200 Extraction Temp, 150 150 Refined oil yield. vol. percent 75 Refined Oil Tests:

Viscosity, SUS at F 317 265 Viscosity, SUS at 210 F 52. G 5l. Il

Viscosity index Jl. 0 110. 5

Color lovibcnd 54. 20

RI at 70 C 1. 4705 1. 4G80 This example shows that refined oil viscosity index, upon extracting at the same conditions, is much higher with NMP than with furfural.

Example II TABLE II.- 0 VISCOSITY INDEX LEVEL Conditions:

Solvent Furfural NM P Solvent dosage 400 Extraction temperature, F. 152 140 Refined oil yield, vol. percent 73. 5 78. 5 Dcwaxed Rafnate Tests:

' 353 378 Viscosity, SUS at 210 F 54. 3 55. 7 Viscosity index 89. 5 90. 0

our, +10 +15 Color, lovlbond l/ 45 40 100 VISCOSITY INDEX LEVEL Conditions:

Solvent Furfura. NMP Solvent dosage. vol. percent 660 202 Extraction temperature. F 185 140 Refined oil yield, vol. percent 59. 7 72. 7 Dewaxed Rafnnte Tests:

Gravity, API 29. 5 29. 4 Viscosity, SUS at 100 306 252 Viscosity, SUS at 210 F- 53. 0 49. 8 Viscosity index 100. 0 100. 0 Pour, F +10 +5 Example III A fraction separated by vacuum distillation of a naphthenic crude oil referred to as 300 Pale Stock is treated with NMP at the conditions shown in Table III following:

TABLE IIL-PROCESSING CONDITIONS Solvent dosage, volume percent 150 Extract outlet temperature, F. 140 Ranate outlet temperature, F. 171 Refined oil yield, volume percent 81.6

Charge and product tests are given in Table IV, following.

This example shows that the refined oils exhibit superior color, color stability, corrosion and thermal stability characteristics when compared with the unrened oils.

TABLE IV.CHARGE AND PRODUCT TESTS Basic N 2, p.p.m Sulfur, Wt. pement' Color, Lovibond:

Initial, 6 After 24 hrs. at 220 F., 6"..- After 24 hrs. at 220 F.

liovibond y at 70 C SOD lead corrosion 325 F.,l wt. change:

MgJin.2 at 1 hr 6. 6

Mg./in.2 at 6 hrs -48. 6 Toettcher varnish 13 hrs. at 305 F4 Varnish, mg 184 Viscosity increase 210 F., percent... 100

Neutralization no 6. 8 Heat test, 125 hrs. at 400 Fal Evaporation loss, percent Viscosity increase CS at 210 F., percent. 73. 5

Neutralization No 95 Sludge None l The S.O.D. Lead Corrosion Test is a bench test of corrosion resistance which is described in Military Specification MIL-L-708C, Lubricating Oil, Aircraft Turbine Oil,

Synthetic Base dated November 2,` 1955 and is described in detail in U.S. Patent 3,003,963.

2 The Toettciler Varnish Test is a high temperature deposit test described in detail in U.S. Patent 2,674,577.

The Heat Test is a bench test for thermal stability in which a 250 milliliter semple'of the oil under test is heated for 125 hours at 250 F. and then held at room temperature for 1 day. The sample is then weighed to determine the evaporation loss, the viscosity is determined and compared with the oil before heating, the neutralization number is determined, and the presence or absence of sludge is noted.

Example IV A vacuum distillate from a paraiinic crude oil identified as a Wax Distillate is refined with NMP at 150 volume percent solvent dosage, 157 F. extract outlet temperature and 210 F. raiinate outlet temperature to produce a yield of 68.6 volume percent of refined oil. Tests of the unreiined charge, refined oil and extract product are listed in Table V following:

TABLE V Refined Charge oil Extract Gravity, API... 25. 3 30. 0 15. 4

Y After 24 hrs. at 220 F., 6 Carbon residue, wt. percent.- Ash, wt. percent Neutralization No. Sulfur, Wt. percent- Basic Nr, p.p.m

The reined oil is then dewaxed to a 5 F. pour in order to show the eiect of NMP refining on the corrosion, oxidation, and heat stability of Ithe oil. A comparison of the unrefined dewaxed oil and the NMP relined de- `waxed oil is shown in Table VI, following.

This example shows that the NMP rened oils have lighter colors and improved color, corrosion and thermal stabilities as compared with the unrened oils.

TABLE VI Unrened Dewaxed Tests:

Gravity, API Flash, COC, F

Carbon residue, wt. percent. Neutralization No uliur, Wt. percent. Color. Lovibond 6:

Inital 1 After 24 hrs. at 220 F Lovibond l' 52. f! 40. 4 Mg/ln.2 at 6 hrs 436 248 Spindle oil oxidation 24 hrs. at 250 2 Saponification No 2.8 3. 1 Neutralization No 74 Viscosity increase, J F., percent l2. 6 11. 3 Heat test hrs. at 400 F. evaporation loss percent 3 0. 8 1. 3 Viscosity Increase:

CS at 210 F., percent 35. 9 2l. 0 SUS at 210 F., percent. 23. 6 11. 2 Neutralization No 1. 6 1. 2 Sludge None None l The S.O.D. Lead Corrosion Test is a bench test of corrosion resistance which is described in Military Specification MlL-L-70RC, Lubricatmg Orl, Aircraft Turbine Oil, Synthetic Base, dated November 2. 1955 and is described in detail in U.S. Patent 3,003,963.

i'Ttie Spindle Oil Oxidation Test is a bench test for resistance to oxidation. The oil under test is heated in the presenee of steel, copper, and lead strips for 24 hours at 250 F. with air bubbled through the oil. The increase in viscosity, the saponiiication and neutralization values are then determined.

3 The Heat Test is a bench test for thermal stability in which a 250 milliliter sample of the oil under test is heated for 125 hours at 250 F. and then held at room temperature for l day. The sample is then weighed to determine the evaporation loss, the viscosity is determined and compared with the oil before heating, the neutralization number is determined and the presence or absence of sludge is noted.

Example V A comparison of the solvent extraction characteristics of NMP with another gamma butyroiactam, Z-pyrrolidone for lubricating oil refining is made by parallel extraction at the same conditions of a low viscosity lubricating oil stock and a similar comparison is made with an intermediate viscosity lubricating oil stock. It is found that 2-pyrrolidone is not as effective as NMP for the improvement of viscosity index of lubricating oil stocks in that less than one third of the amount of extract oil is removed from the refined oil at the same conditions of temperature and dosage. A greater reduction in the refractive index of the rened oil is obtained with NMP and the reduction in refractive index in treating the intermediate viscosity lubricating oil stock with NMP is greater than in treating the low viscosity lubricating oil stock.

We claim:

1. In the manufacture of lubricating oil, the process which comprises distilling a crude oil separating a vacuum distillate, contacting said vacuum distillate with a solvent consisting essentially of Nmethyl2pyrrolidone at a temperature of at least 50 F. and below the temperature of complete miscibility of said vacuum distillate in N-methyl-Z-pyrrolidone and at a dosage effective to dissolve at least 10 volume percent of said vacuum distillate forming a refined oil of improved viscosity index and improved inhibitor response, dewaxing said rened oil as necessary to produce a base oil of reduced pour point,

10 late is from a paraflin base crude and'has a viscosity index within the range of about 40 to 105, and the viscosity index of said lubricating oil is 'at least 10 units higher than said vacuum distillate.

15 References Cited UNITED STATES PATENTS 2,092,739 9/1937 Van Dijk 208-326 2,761,814 9/1956 Post 208-36 20 2,767,119 10/ 1956 Forchielli 208-289 2,933,448 4/1960 Morin et al. 208-326 HERBERT LEVINE, Primary Examiner 25 Us. c1. X.R. 

